The present invention relates to an improved vehicle body frame technique.
In vehicles, vehicle body frames are known in which hollow frame members such as side frames extending longitudinally along a vehicle body are provided (for example, refer to Patent Literature No. 1).
[Patent Literature No. 1]
JP-A-5-65076 (pages 2 and 3, FIGS. 1 and 6)
According to Patent Literature No. 1, a conventional vehicle body frame is such that longitudinal and transverse ribs are integrally formed within a hollow frame member such as a front-end or rear-end side frame extending longitudinally along a vehicle body. When a vehicle is subjected to a front-end or rear-end collision, the hollow frame member plastically deforms so that crash energy can be absorbed.
In the conventional vehicle body frame, the hollow frame member buckles and deforms in a bellows-like fashion from a distal end thereof when crash energy is applied to the distal end of the hollow frame member. The larger the hollow frame member deforms, the more the crash energy can be absorbed.
Incidentally, it is known that after the hollow frame member is deformed to a certain extent, a larger force than that applied before is required to deform the hollow frame member further. This still requires a further improvement to be made in order to increase the absorption of crash energy.
Then, an object of the invention is to provide a technique which can increase further the absorption of crash energy by the hollow frame member.
With a view to attaining the object, according to a first aspect of the invention, there is provided a vehicle body frame characterized in that hollow frame members such as side frames which extend longitudinally along a vehicle body are provided thereon, and in that two inner partition plates are formed integrally in the interior of each of the hollow frame members in such a manner that the two inner partition plates extend in a longitudinal direction of the frame member and are close to each other along plate surfaces thereof, so that a central space portion defined by the two inner partition plates therebetween is formed in the interior of the hollow frame member, whereby side plates constituting the hollow frame member can be dissociated at portions of the side plates which face the central space portion by virtue of a buckling load.
The hollow frame member can be dissociated at the portions of the side plates constituting the hollow frame member which face the central space portion by virtue of a buckling load.
Consequently, when the hollow frame member plastically deforms in a bellows-like fashion by virtue of crash energy applied to the longitudinally distal end of the hollow frame member, the two inner partition plates are caused to strike each other so that the side plates can be broken at the breakable portions, whereby the hollow frame member can be dissociated into two parts from the breakable portions so broken which act as a boundary. The buckling strength at the dissociated portion is extremely smaller than the buckling strength of the hollow frame member before it is dissociated. The size of the hollow frame member that remains after it is deformed can be decreased further. As a result, the absorption of crash energy by the hollow frame member can be increased further.
According to a second aspect of the invention, there is provided a vehicle body frame as set forth in the first aspect of the invention, where in the side plates constituting the hollow frame member each have a frail portion formed at the portion which faces the central space portion.
By forming the frail portions at the portions of the side plates constituting the hollow frame member which face the central space portion, the breakage of the side plates at the breakable portions can be facilitated.
According to a third aspect of the invention, there is provided a vehicle body frame as set forth in the first or second aspect of the invention, wherein a rib is formed on the plate surface of at least either of the two inner partition plates.
Since the rib is formed on the plate surface of at least either of the two inner partition plates, the rigidity of the inner partition plate can be enhanced. When the hollow frame member plastically deforms in a bellows-like fashion by virtue of crash energy, the inner partition plate can be caused to plastically deform in a more regulated waveform-like fashion.